Isopropanol quality improvement process



s. w. wlLsoN 2,696,508

ISOPROPANOL QUALITY IMPROVEMENT PROCESS 3 Sheets-Sheet 2 Dec. 7, 1954 Filed Sept. 21. 1950 1 T1 9 m 4- (Du- N 5 E c l m C m r w 3v) H :5 8 T F O L o Samuel ufwilson." anvermor fQg Clbboiqeg Alkali.

Dec. 7, 1954 s. w. WILSON 2,696,503

ISOPROPANOL QUALITY IMPROVEMENT PROCESS Filed Sept. 21. 1950 s Sheets-Sheet :s

P H l k & T

q i 4.) ,2 g; 5 :2 l W c 'H Samuel UJfUUTlsoa Unverlbor @g Clbborrleg 2,696,508 Patented Dec. 7, 1954 ISOPROPANOL QUALITY INIPROVEMEN T PROCESS Samuel W. Wilson, Baton Rouge, La., assignor to Standard Oil Development Company, a corporation of Delaware Application September 21, 1950, Serial No. 185,915

1 Claim. 01. 260-643) It is another object of this invention to set forth a process for the production of prime grade isopropanol free of malodorous impurities.

It is well known that alcohols, particularly those produced by the acid-catalyzed hydration of olefin hydrocarbons, possess a distinct and apparently foreign odor,

slightly penetrating and for the most part disagreeable. While no attempt will be made to definitely assign the disagreeable odor of alcohols prepared by olefin hydration to the presence of any one or combination of chemical compounds, it can be said with reasonable assurance that the odor of crude alcohol depends to a large extent on the quality of the olefin stream employed in the olefin hydration operation. Likewise, the odor of a refined alcohol depends to a large extent on the quality of the crude alcohol from which it is prepared.

Olefin hydrocarbons, such as those produced by the cracking of mineral oils, contain variable amounts of compounds having an obnoxious odor particularly sulfur compounds such as hydrogen sulfide, alkyl sulfides and mercaptans. These materials present, even in minute amounts, in the olefin stream to the sulfuric acid-catalyzed hydration process are believed to contribute to the obnoxious odor of the crude alcohol since, while sulfur alone has no smell, it is clear that in combination with other elements it is a powerful odoriferous agent.

The bad odor of alcohols has also been attributed to the presence of so-called high-boiling polymer products formed in side reactions during the alcohol process. The odor of the polymer products is strengthened by the presence of any sulfur compounds dissolved therein, although the odor of some of the pure polymers themselves is by no means pleasing to the olfactory sense. A typical analysis of a sample of the so-called polymer product, in this case the so-called propyl oil, resulting from the production of isopropyl alcohol by the sulfuric acid-catalyzed hydration of propylene, is as follows:

The composition of the propyl oil or so-called highboiling polymers obtained during the concentration of dilute crude isopropanol varies according to the point from which the alcohol containing it is withdrawn in the concentrating tower, and the odor likewise varies.

Cuts can be identified with an odor of camphor, of menthol, etc. It has also been reported that the presence of nitrogen compounds also contributes to the odor of alcohols.

The odor imparted to isopropyl alcohol by the propyl oil impurities is a hydrocarbon type odor. This type of odor has been found to be efiectively removed by a number of methods such as by careful and repeated conventional fractionations, but particularly by the water extractive distillation method as described and claimed in U. S. patent application Serial Number 24,626 filed May 1, 1948, now Patent No. 2,638,440, and assigned to applicants assignee. However, there is a second type of odor which is fugitive in nature and which may best be characterized as a mercaptan or thioaldehyde odor, and which is attributed to the presence of low-boiling sulfur compounds such as mercaptans or thioaldehydes which appear to bedecomposition products of higherboiling impurities which break up under alcohol purification-distillation conditions. It has been found that this second type of odor is particularly noticeable when the alcohol production process is operated under upset regenerator conditions or when the purification process is operated under upset concentrator conditions. When the capacity of the regenerator or concentrator is exceeded some isopropyl alcohol creeps down into the reboiler associated with the regenerator or concentrator wherein a high temperature prevails and where a particular concentration of sulfuric acid exists. Under these conditions it is felt that the sulfuric acid present in the reboiler acts as a reducing agent on the isopropyl alcohol which decomposes into lower-boiling impurities, particularly mercaptan and/or thioaldehyde compounds which are volatile. These impurities go overhead with the alcohol from the regenerator. Subsequently in the concentrator they are not all removed with the lowboiling overhead, but remain in traces of parts per million in the isopropyl alcohol product which is removed as a top sidestream from the concentrator. Likewise if the concentrator conditions are upset the same decomposition occurs and the problem becomes aggravated. It has also be theorized that the second type of odor is due to the decomposition of sulfurized esters which are formed in minute amounts during the propylene absorption in sulfuric acid. These esters are thought to decompose either thermally or by hydrolysis.

Furthermore, there are indications that some of the malodorous compounds are rather strongly bound in the aqueous alcohol product in such a manner that they tend to concentrate along with the alcohol during such alcohol finishing operations as solvent extraction heads removal, water extractive distillation, and concentration. However, the nature of the chemical reactions tending to bind these malodorous compounds is such that unstable addition compounds result and the malodorous compounds are liberated and volatilized to some extent during all alcohol finishing operations of the types described. For instance, in typical alcohol finishing operations the following problems are encountered. Crude alcohol, after passing through the heads operation to remove ether and other low boilers, is fed to a finishing column in which certain low-boiling materials are taken overhead with a purified alcohol taken as a sidestream. Materials contributing to recycle odor appear to be lower boiling than the alcohol proper but are nevertheless not completely removed from the alcohol sidestream. This result is believed to be due in large part to the fact that decomposition reactions liberating low boiling malodorous compounds occur during the distillation, allowing these malodorous compounds to pass overhead. Similar difiiculties are encountered when applying water extractive distillation to the same crude alcohol. In fact, water extractive distillation appears to concentrate the compounds giving rise to mercaptan odor along with the alcohol so that, in the final alcohol finishing operation, an alcohol product high in mercaptan odor is obtained. This seems to be particularly true of isopropyl alcohol prepared by the so-called weak acid method as described below.

It has now been found that isopropanol of improved odor quality can be produced by treating the crude alcohol with an alkalizing agent such as the alkali or alkaline earth oxides, hydroxides or carbonates, organic amines, etc. until a pH of above 8.0, preferably 10 to 11, is obtained, reacidifying the alkaline crude with phosphoric acid or P205 to a pH of 2.0 to 6.9, preferably 5 to 6.5, and thereafter recovering the alcohol from the reacidified solution. If the original crude alcohol is its. pH exceeds 8.0. If it [is neutral it still must be brought up to the required allgaline pH. If these prerequisite'conditions' are not sati tie-d treatment with p'h-os' pho'ric acid has less "effect." TreatmentWithsuIfuricacid and/ or sulfurous acidinste'ad; of phosphoric-aciddoesi not improve the'quality. of"therecovered alcohol.

After the crude aqueous isopropanol hasbeen 'aciditied with phosphoric acid the alcohol is recovered by. any of a number of lternative' methods' such as by solvent. extraction of the'alcoh'ol with solvents insoluble in aqueous'alcohol, e. g. 'aliphaticethers, .by conventional fractional' distillation methods involving .customary'hea'ds removal followedby concentration, by stripping,"- or .by. water extractive distillation, etc.

Crude isopropyl alcohol maybe-produced by the sulfuric acid-catalyzed hydration or propyleneby thewea'k acidrnethod' or thef'strong acid method; Inthe-former process a relativel' richpropylene stream containing about '50-80 volume-per cent'propylene is absorbed in sulfuric acid'of approximately 60 to 80weight per-cent concentrations, preferably 70 weight-percent 'at a'bo'ut" 170F. and approximately 250 pr s. i. erressure form' an extract comprising 'isopropyl sulfate 'Which"isf partially hydrolyzed to-- alcohol during the absorption."

Thehydrolysis ,is completed by .dilution' of the 'extract with water to approximately 45 wt. per'centacid strength,

with 1 or without a soaking" period which entails maid" taining the extract at a temperature of"about' l90 F. for a periodof about minutes'residence "time. The

hydrolysis products are then'distilled in an alcohol regenerator wherein crude alcohol vapors are removed overhead subsequent re-use in the absorption process? Theicru'de isopropyl alcohol contains approximately30-60%jby volume of isopropybalc'ohol, some impurities i'ncl'udi'ng ether, .acetone a'nd unknownfi H and condensed, and wherein spent .sulfuric acrd is recovered as bottoms; for 'recon'centratlon andess a propylene stream of relis-Cont'acted undersimilar i con-i ditions v'vi th' 'astronger sulfuric acid e xg 'acid-of SO9'S- weight per cent concentration, preferably SST-88;: weight per cent, whereby an extract is formed as" above. The

extract goes through a similar hydr'oly'sis and *strippin'g'j" scribed 'for" the weak acid e tionalfractionation} it -is led to a 'headsQ colum purpose of which is to remove etherand'other lOW-bblP known impurities.

withdrawn overhe'ad while weak aaqueous alcoho -1s" r covered as bottoms. Th'e weakaqueousalcohol distilled in a concentrating"column-' whereFthe' alcohol is c'oncentratedto a composition-' approaching it water per cen't isopr'opyl alcohol 9 vol, The alcohol of azeotropic=compos1t1oh azeotrope, vi'z.,' 91 I vol.- per cent" water. maybe further distilled forremova'l of"ace'tone, if pre sthen entfor concentrated further to 95';volI- perfcentf'or 99;

vol." percent isopropyl "aleohol if desire dl by'extractive distillation such-as is describedinsertar;

above, the" crude a'lcoh ol is dis No; 24,626 referred "to tilled countercurrent toan internal water-reflux containf water, preferably 80 95 m ing'70-99 mol. percent per' cent, whereby the low'jboiling impurities both Water soluble and water-insoluble: and. some; of the" high-boil- -&

ing impuritie'sare removed .over heaiuwhilefla dilute; aqueous solution of the alcohol s recoveredas bottoms and sent to a concentrating column. where azeotropic alcoholis separated as a' topsidestream-from thebalance;

of the high-boiling impurities andfwate r.. v

The process may be .bette'r ,understoodvvhen read in conjunction with the f accompanying drawings which l'epresent-diagrammatic elevational views of equipment 1 and l flowj of materials in the processes. v

Figure; 1. a fl s qf er ts s sa qyi s averiti'onal distillation methodsfor ls opropanol recovery.

Figure 2 illustrates recovery process employing Water extfifiife disfill'aftifim'"While Figure 3"i.'[1u'SfilfS' the "S'O'F' vent extraction recovery method.

Referring to Figure l, crude aqueous isopropanol is introduced to the heads column 6 through line 1. Caustic is preferably added throughline 2 to adjust the pH of the alcohol to above 8.0. Phosphoric acid is introduced from" tank through? lines 13,. .4, ions; or; 21 combination of theselines to'. Ioweri'the pH of the contents ofv theheads column to 2.0 to 6.9, preferably 5.0 to 6.5, Ether and "othenlight endsare 1 distilled overhead from" colt1'rnn-6 via' lin'e "7 through-'-condenser'- 8 to accumulator 9. A portion of the overhead may be returned as reflux .via linev 10 to column 6 and the. remainder or to ether washer 42.. Water is introduced via line 13 to dilute the overhead to washer 12 in sutficient amount to cause phase separation of ether and aqueous alcohol. Product ether-is drawn offithrough -line 14-anda portion mayberecyc'ltad to washer-12"via -line.15. to improve. washing. The ether washer. bottoms are...return'ed to heads'column 6'via line l6 or30 atany-one-of-several: points 'in the towen It' may be returned via lineinlil Open steam or a reboileri'is used-to" introduce heat to the heads column. The bottom from Ithe heads column is.- fed to the concentrating and fractionating columnlfi; throughline-17. Preferably caustic is injectedinto the bottoms from the heads-column from tank throughline 19in sufficient amount to make. the stream alkaline, preferablyto apH of 10.5'. The caustic may be introduced via line 20 into the alcohol column at some point. above 'the feed"in suflicientaamount to raise thepH of the liquid on the'trays and the bottoms frornthe column. above 8.. High'iboilers arewithdrawn from the. bottom. section ofJthe alcohol column zfrom' zonesi above and/or below the feed point athrough linei :21. and introduced into-. the ether wa shen.12m here inthepresenceiof sufii-f. cient .water; phase-separation takes'l'placexand .the:highi. boiler-s i areextracted;lwithi';the ether.'.; Eitheri'openi stea'nrf. or a r'eboilerimay Lbe use'd to supply heat'stoa-thei alcohol column. Water. is =witlfdr'awn': fromiftheL'bot-tom of the alcohol column .via lin'ei'22. .Thefl9 1% isoprop'ano'l ia-zeo-Ivv trope {plus acetone. and tether-slow .boilinguwatersoluble compounds; .e. g." aldehyde, :are: taken: overheaddn fool-. umn' 18: throughxline 23 andtzcondensedi- Aiportidn. f the overhead. is-pumpedi iback-as r'efluxizthrough line'24' and the bala'nceiis fedr to the"acetone column:25 :through line-'26; ,9 A'ceto'ne' ;ando'ther possible-light vtends tareptakenz overhead from column...25 through' linev27; A portion of the overheadis pumped back: as reflux-"and: the balaance is .-sent:to storage .asa lowengrade isopropanoltor cru'deuacetorie through liney28-.='.-.. Product :.sisopropanol is taken 'as bottoms. through;- line. 29. r Heat is'..-.supplie t'o.; column: 25byrrneansl;of.-.a'reboiler...

Referringrnowztol Figure 2 thenpurificationlof Tisopro-l. panol Zby'. .iwater-g extractive? distillation frwill ibe :sdescribed Crude aqueous lisopropario fed; to. theeiheadss'colum 6 throughlline:-1-.' Caustic. s added;eitheeiingtheicrud SEQtiOlILOI' through: lineg'2 to. makei .the pH above 218.0 Phosphoric;.acid*suflicientiitdrattainz a pH'Jof -2i0 .t'o :.6.9 preferably; 5 .O' .t'o. 6.5. isv theneadded to dhencru'dei fro tankvP throughline. 3io'r by-passAvia liIlCiiI-OEL'. Y. Wate asgt :extractiveamediumZis;introducedsto:the extractiy. or;.heads columhvia-lindufii and: 10. Thel-overhe'adus taken via line'.7, condensed; :in; condenser: 8; and:-'pumped-.-; from accumulator 9 to the ether washer 12 via line 11. A portion may -be returned as rnninmmgnnine; 10. The bottoms -fronrflthe"ether wash s' retur'-ried--to t'he heads col mn via line-'16f and -10. 'Water-is added'to the ether wa'sher via line'l3 and phosphoric acid rr'iay'i be injected at this point -via lines 5- and 1 5 Ethelr prodnot is Withdrawn via line 14 and a portion rr'ia'y' be re-- 15 to the ethenwasher The; dilute, aqu l bottorris fromhe Ehea'ds D Q IT. p lpo nt onxit eIfin s with the'process;of" Figure""1.' Alkjali, droxide; ,isi'prefe'rablyf added to f.the',.l;b

" icommmviagme:.19ifrom..taak N 1 s vage shww crude isopropanol' is illustrated in the flow diagram. of Figure 3.

Referring to Figure 3, the crude aqueous isopropanol enters a liquid phase countercurrent extraction vessel 32 '6 Commercial scale tests were also conducted and the results obtained in the laboratory tests were confirmed. The plant tests were made over a period of 3 to 8 hour via ligefil. Water i added hto extractor 32 xf/iaflline 33 v distillation time. During these tests the products were in su c1 ent quantity to give p ase separation o e or an t high boilers from the crude alcohol. A water-insoluble ed as erede 1 m an m-Sumees Whlle pnor and after Solvent Such as isopmpyl ether or hydrocarbon, g. t e test period (phosphoric acid shut ofi) the lsopropanol pentane, is injected into the bottom of extractor 32 via was gl'adfid as low as 4, Which is the lowest Possible gsitg -iscglfggg 581 3235 1 2 680 612 3: Sign? ii g-t grading. Typical data from the plant runs are given in c e r c or is fed to the first column 6 (or heads column) via line 1 or Table Durmg these epeeatlons the PH the ,heads phosphoric acid from tank P is added to the crude column bottoms separated with water extractive distillavia line 3 or rrdiay the intrgduceg via t1line 44 in sufficient tion conditions or semi-extractive conditions was lowered amount to ren er e cru e aci to e extent previously recited, preferably to a pH of 5.0 to 6.5. The alcohol from H m the T of to 11 to a T of 16.11) from the crude section is made alkaline to a pH greater with phosphonc The phosphonc and was than 8.0 prior to acidification with phosphoric a id. troduced to the system via the heads column reflux drum. 32:; lsg ggl lz ggi g x ggy %s g gd aifi tg gtgf sg 2O Essentially all of the heads column overhead was pumped line 44 and line 33. The ether containing the extracted from the reflex drum to the ether Washer and the ether materials is withdrawn via line 37 and a portion recycled Washer boltoms (P to were returned as mfluX viiadlne 381. Ellganeflgl or riedistilileil solgeiit may1 be to the top of the heads column along with some hot a e via ine i tensan ow oiing diute 1 alcohol soluble materials or soluble materials of higher l f if' In flgesebruns It not fund neceseary to relative volatility than dilute aqueous isopropanol, meet caustl Into t e .ottoms the heads column, concentration, preferably 15%, are taken overhead from (feed is the alcohol concelltl'atloll This is salsa: arteries 35223312 222 ;%..$2hfti? 3 3; ;3535,3 z gg ggg ggg g gg g w The balance of the flow is the same as Figures 1 and 2 30 as no with alkali being added from tank N and line 19 to the possible to re ect high boilers overhead during the heads feed to the concentrating column in line 17 to render the operation or via side streams. There was no evidence stream i pmfembly to a PH about Pnor to of corrosion based on copper and iron analyses of the concentration of the alcohol. h d 1 b d th th The invention is illustrated by the results of laboratory 35 ff 5 co umn cttoms an e e er Washer bottoms runs set forth in the following tables: 5 cams- TABLE I pH control and product quality of isopropanol Run Number X5OA X500 X5013 X5013 XF Initial pH of Crude 3. 3. 3- 3.3 3.3. Treatment of Crude None NaOH to 10.5 pH.--

{8 951 5: HaPOt to 5.0 pH None. Treatment of Bottoms from None None NaOH to 10.5 pH NaOH to 10.5 pH NaOH to 10.5 pH,

Heads Operation. Product Quality 4 Rand H. 3 B. 1% 3 B. 3 R. Remarks Finished in plant 3 H Slightly less than Grade 1.

Product Quality:

R= Recycle odor. H=Hydrocarbon odor. B=Butyl odor. Grades 1 and 2=Prirne grade. Grades 3 and 4=Regular grade.

TABLE II pH control and product quality of isopropanol XGOA XGOE R1111 Numb r XSOA (G heck Run) XGOE (Check Run) X6013 X600 XGOD Initial pH of Crude- 8.6.. 8.6.. 8.6- 8.6 8.6 8.6, Treatment of Crude 10.5 pH with 10.5 pH with 5.0 pH with 5.0 pH with None None 10.5 pH with NaOH then NaOH. then H P04. aP t. NaaPot. 5.0 pH with 5.0 pH with B 1 0 HaPO4. Treatment of Bottoms from 10.5 pH with 10.5 DH with 10.5 pH with 10.5 DH with .---.do pH with None,

Heads Operation. N aOH. NaOH. NaOH. N 21011. azPO Product- Quality; 1 1 3 R and 13--.. 3 R and B.--. 3 B 4 R, Remarks Equivalent to Equivalent to This is the blank heart out heart out run. This crude from redisfrom redisfinished 3 H in tillatlon of tillation of the plant. Grade 1 9.1- Grade 1 alcohol. cohol.

Product Quality R= Recycle odor.

H =Hydrocarbon odor.

B Butyl odor. Grades 1 and 2=Prime grade. Grades 3 and 4= Regular grade.

aeeaws Odor o i Product new i Run Nahv Re'zi'zarks Phosphoric acid started at 8:10

Heads column bottoms less than 610 pH. Samples at V hr. intervals, all

Grade L 'One=halfhour' after acid was u fi Composite for I period 8:45 V a. m-.. 2:00 p. m., Grade 1-.

Phosphoric acid started at 8:05

5 :00 a. in 3R and H a. m.,- pH 11.0 before start. 8:00 a. In 3 R and H pH 4.0 to 6.3 maintained dur- 8:15 a. m 2 H ting balance of run.

"""" 8:30 a. m 3 R and H Samples were taken at 20 to 30 8:50: minuteintervals. 8:50 a. m.- 4103 p. m.- v1 4:03p. m All Grade 1. Acid 11 so 4 R d H out off at 3:42 p. m. .1 a.m ..-v an t a n rsatz"; repeaters: g g and H bottoms before starting acid. 1 pH hea'ds-botwms 3.6-6.0. 3. 1.30 1 Do lffl) '1 1 2:10 1 2:40 1 3 D 3:10 a 1 Iii grading isopropanol as reflected by the'rati'rigs in the tables, the following is the meaning of the numerical ratings:

Grade 1-A1cohol with no foregin odor. Grade 2-A1coho1 with a very slight foreign odor.

.8 Gradefi--Aloohol with a moderately noticeable. 0d01' Grade 4-Alcohol containing appreciable to excessive amounts of foreign: odor. H"'vingide's'c'rib'e"cl the invention in.a manner such that if may be racticed by those skilled in the art what is clairn'ed-is:

A process" forrefim'n'gcrude aqueous i'sopropanol preparedby sulfuric acid, catalyzed-hydration of propylene,

said crude isop'ropanol being characterized by the presonce of undesirable odors of sulfur compounds and hydrocarb'o'n impurities, which comprises adding to said crude isopropanol sufficient alkali to give the crude alcoliol apH in the range of 8.7 to 11, then acidifying the alkaline crude isopiopanol' withphospho'rie acid until the i'sopirbpanol' has a pH of 5.0 to 6.5 prior to distillation of saidjcru'de isop'ropanol with alkali, then distilling the acidified crude isopiopan'ol ,to removc therefrom. irripuritiescornpr'ising' lowjbo'ilir'ig' andv high boiling impurities, treating the acidifiedcr'ude i'sop'ropanol residue from which said impurities are distilled until the isop'rO- panel is rendered alkaline, and distilling refinedi'sopropanel from .the' isoprbpanol residiie tenderedalkaline References Cited in the file of this patent STATES PATENTS Nuihber' Name. Date 2,080,111 Buinp May 11, ,1937 254L673. Smith Feb. 13, 1951 FOREIGN PATENTS Ndr'nber Country Date 350,502 Great Britain l June- 15, 1931 

